1. Field of the Invention
This invention relates to a plant sheet for covering rock surfaces, concrete surfaces, and bare grounds and a method for manufacturing such a plant sheet.
2. Description of Related Art
Greening provides relaxation from the so-called heat island effects in urban areas, improvements in air environments by direct absorption of CO2 through trees, and habitats for growth and nurturing of various creatures. Because spaces with greens and waters bring natural feelings to human beings, coverage with greens over concrete wall surfaces, soilless rock surfaces, and bare dried grounds provides a more suitable environment for people living thereon. According to recent experiments, a greened surface on the roof of a building generally results in a lower greened roof surface temperature, e.g., about 15 degree Celsius less than that of a comparable concrete roof surface. Additionally, the green roof surface keeps warm during the winter time and cool during the summer time. Greening has a significant impact on a variety of creatures, such as insects and birds that can live well even on a greened roof area of a building, which would otherwise be covered with concrete surfaces.
Greening by incorporation of plants may provide better scenery to not only urban areas but also newly developed areas, undeveloped areas, roads and riversides. When a new road is extended through cutting mountain areas, portions of the area immediately surrounding the road would be soilless rock surfaces and concrete surfaces. Such artificially created surfaces sometimes lack harmony with natural surroundings, but when filled in with plants by greening, such bare grounds and soilless rock surfaces, become desirable green surfaces for regaining the natural harmony.
Plant sheets, tapes, and trays have been known for covering such artificially created surfaces. Plant trays having a depth for keeping soil can be arranged in multiples on a roof to make the roof green. In a typical case, each tray is in a rectangular or square shape and contains soil for growing plants. Such plant trays, however, raise the following problems: First, the plant tray is generally available in a standard size, and when a roof is fully covered with such trays, gaps and open spaces can exist at the edges. Second, partly cut trays can not be used as they are not operable due to the inability to hold soil or water within the cut section of the trays.
There are plant sheets that are of a free size and can fit and mold to any area, because the sheet can be cut according to the dimensions of the area the plant sheet will be attached to. Such a plant sheet also holds the soil from which the plants grow. However, some plant sheets serve only for mulch purposes, or preventing water from overly evaporating and the plants from receiving frost damage. Such a mulch sheet generally does not have germination facilities, and therefore, seeding is required for plant growth in addition to placing the plant sheet on soilless surfaces such as concrete surfaces. Some plant sheets have a soil layer from which germination and cultivation of plants is possible, but addition of a soil layer requires extra manufacturing steps and could increase the price of production. The soil layer in the plant sheet also makes the plant sheet heavier and thicker and therefore makes handling by the operators uneasy.